Shrouded parabolic antenna structure



W U m W PM A E \w Nov. 7, 1967 J. w. HART SHROUDED PARABOLIC ANTENNA STRUCTURE 2 Sheets-Sheet 1 Filed Feb. l7, 1965 N 7, J. w. HART 3,351,947

SHROUD ED PARABOLIC ANTENNA STRUCTURE Filed Feb. 17, 1965 2 Sheets-Sheet 2 Inventor- Ja mes W. H'nr'fi mm & we

ifi' rnew United States Patent 3,351,947 SHRGUDED PARABOLIC ANTENNA STRUCTURE James W. Hart, Highland Park, Ill., assignor, by mesne assignments, to Mark Products (Iornpany, Skolrie, Ill., a corporation of Illinois Filed Feb. 17, I965, Ser. No. 433,288 Claims. (Cl. 343-840) This invention relates in general to high frequency antennas and more particularly to an improved parabolic antenna having a light weight, weather tight, self-supporting radome cover with associated internal reflecting shroud effective to enclose the face of the dish reflector and, improve the radiation directional pattern, and avoid leakage.

The advantages of parabolic antennas in high frequency point-t0 point communication systems are well known. Such antennas, when properly constructed, exhibit an extremely high front-to-back ratio and consequently high gain. Relatively little radiant energy is transmitted in the minor lobes so that a sharply defined, narrow beam of energy is obtained.

There are, however, certain inherent disadvantages. For example, such antennas are usually placed high above the surrounding terrain, and are thus subjected to substantial wind loading, as well as being exposed to severe environmental extremes, which may vary the energization of the dish reflector. Such variations, even though slight, detract from the otherwise optimum performance characteristics and result in undesired side and back radiations.

Solid metal reflecting shrouds encircling the periphery of the reflector dish have heretofore been used to suppress radiation to the side and back. However, the need to withstand wind, especially under conditions of rain, snow, sleet and ice, in addition to the need for an effective reflecting shroud, had made it difficult or impossible to reduce weight and size of the overall structure. Since support must be achieved outside the radiating beam, such antennas have required heavy, expensive support struc ture. In addition, these radome enclosures usually span the open end of the shroud with a flat disc of suitable material of low loss characteristics. Because of the flat-faced configurations, such discs develop maximum wind resistance to head-on winds. Moreover, such discs are in the nature of diaphragms that contribute little, if any, structural strength and do not contribute the required rigidity of shroud and antenna structure. In some instances, substantial leakage radiation has been encountered between the reflector dish and the bottom edge of the reflecting shroud.

Accordingly, it is an object of the present invention to provide an improved high frequency shrouded dish parabola antenna structure characterized by light weight and favorable radiation performance characteristics under all operating conditions.

It is another object to provide a parabolic antenna having a weather tight, radome cover of low loss material totally enclosing the face of the reflector dish and defining a shroud in such fashion as to minimize the effects of wind loading and provide a light weight, self-sustaining structure requiring relatively small supporting structure.

Another object is to provide a parabolic antenna with a weather tight, radome cover of low loss material totally enclosing the face of the reflector dish and constructed of a light weight, mechanically rigid material in a formed self-supporting unit and having a cylindrical shroud portion with an interior surface of a conductive material extending perpendicularly from the periphery of the reflector dish to at least the focal point thereof and in which spurious radiation is avoided.

Still another object is to provide a light weight, unitary radome cover for a parabolic antenna wherein a cylindrical portion is atfixed to the periphery of the reflector 335L947 Patented Nov. 7, I967 ICC dish defining a shroud and at its open end is spanned by an imperforate web of a generally convex outwardly conical conformation defining a weather tight enclosure with minimum weight and wind resistance.

Further, it is an object of this invention to provide an improved shrouded parabolic antenna dish reflector in which flexible screen elements coact with a resilient flange gasket to provide a low-leakage, electrical shield between the shroud and antenna reflector.

Still another object of the present invention is to provide an improved shrouded parabolic dish antenna having features of construction, combination and arrangement making it simple, readily manufactured, capable of twopart arrangement for knocked-down shipment and storage, and in which the various parts coact to form an unusually strong, but light weight unit.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and as to further objects and advantages thereof will best be understood from the following description, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a partially broken away top plan view of an antenna structure constructed in accordance with the present invention;

FIGURE 2 is a side cross-sectional view of FIGURE 1;

FIGURE 3 is a fragmental view shown in perspective of a portion of the radome cover;

FIGURE 4- is a side cross-sectional view showing a mounting detail;

FIGURE 5 is a fragmentary side view showing an additional mounting detail;

FIGURE 6 depicts certain antenna radiation patterns useful in the explanation of the operation of the antenna of FIGURES 1 and 2; and

FIGURE 7 is a graphical representation of the resulttant stresses on the cover from Wind loading.

In practicing the invention, a parabolic antenna is provided having a reflector dish mounted on a cruciformshaped tubular support frame. The reflector dish is preferably formed of spun aluminum and the support frame of aluminum piping. The radiation injection of energizing mechanism comprises an inverted S-shaped waveguide section rigidly held in a fixed relation with respect to the reflector dish such that a radiation window or aperture is located approximately at the focal point thereof. A weather-tight cover encloses the front of the reflector dish and energizing waveguide section and is of a construction which includes a cylindrical portion spanned by an imperforate web of a generally conical shape to substantially reduce Wind loading on the overall antenna structure. The cover is preferably formed of low loss plastic, such as an epoxy resin, with embedded fiberglass to give light weight weight and high strength. The cylindrical portion extends from the periphery of the reflector dish to at least the focal point thereof with the interior surface lined with a conductive material, such as aluminum sheeting to form a reflecting shroud. Such shroud acts to suppress side and back radiations that might otherwise occur due to variations in the energization of the reflector dish from other than at the precise focal point and also from any imperfections or distortions that might be present in the reflector dish itself. The cover is supported in part directly by the support frame and also in part by the reflector dish. A flange extends radially from the base of the cover for fastening to the periphery of the dish reflector by a plurality of clamps. The underside of the cover flange is lined with a resilient supported, multi-layer of conductive mesh. This resiliently supported conductive mesh insures positive and continuous electrical continuity 3 between the shroud and the reflector dish at all points around the periphery to prevent leakage radiation.

Referring now to FIGURES 1 and 2, the antenna structure embodying the present invention comprises a dish reflector 11 formed of spun aluminum in the shape of a paraboloid of revolution. As best seen in FIGURE 4, the dish reflector 11 includes a downwardly turned lip portion 11a formed about the periphery thereof, which lip portion is supported at spaced intermediate points by a plurality of perpendicular support posts 120 of generally tubular construction and forming an integral part of a cruciform-shaped support frame indicated generally at 12. The frame 12 also includes a plurality of laterally extending tubular support members 1212. The members 12a and 1211 are preferably formed of aluminum piping and may be provided in integral unitary construction or as separate members suitably joined together by welding or otherwise.

The injection of energizing means for the parabolic reflector dish 11 Comprises a waveguide section 15 of an essentially inverted S-shape configuration having a radiation window or aperture 15a at one end and terminating in a flange 151) at the other end. The radiation windown 15a may be formed of any material suitably pervious to electromagnetic energy. The waveguide section 15 is maintained in a fixed relation with respect to the reflector dish 11 such that the radiation window 15a is located at substantially the focal point of the dish 11. Such position is rigidly maintained by a vertical support member 16 connected between the bottom-most support member 12a and the waveguide section 15 is shown in FIG- URE 2. The member 15 is formed by separate sections 16a and 1612 which terminate in respective flange couplings 16c and 16d and mated by suitable bolts (not shown). I

A radome cover 20 is provided to enclose the front of the reflector dish 11 and a major portion of the energizing waveguide section 15 and thereby provide the desired all-weather protection for the antenna structure 10 from severe environmental extremes. The radome cover 20 is preferably constructed of a plastic material, such as epoxy resin with a re-inforced base of fiberglass so as to provide a light-weight yet mechanically rugged structure which is completely impervious to severe environmental extremes. In addition, such construction provides a relatively low loss material which will not significantly attenuate the electromagnetic energy reflected from the dish 11. A typical attenuation figure is 0.1 db.

In fabrication, the radome cover 20 includes a cylindrical portion 20a spanned at its forward end by an imperforate web portion 2012 so as to define a completely weather-tight enclosure of unitary construction. As best seen in FIGURE 2, the web portion 29b protrudes slightly forward at the center to present a generally conical or convex outwardly shaped conformation. The wall of the cylindrical portion 2% is of sufficient length to extend outwardly to a distance beyond the focal point of the dish 11 when the cover 20 is mounted to the face of the dish 11 in the manner to be hereinafter described.

As seen in FIGURES 3 and 4, the cover 20 further includes a flange portion 260 extending radially from the rear or base thereof. A rim 20d depends perpendicularly from the outermost edge of the flange portion 200. In addition, a hollow, triangular-shaped housing extension 202 depends downwardly from the bottom of the cover 20 to act as a feed clearancechute for the Waveguide section 15. The housing extension 202 has an open side from the rear as viewed in FIGURE 2 through which the waveguide section 15 extends. A cross sectional view of the housing extension is 20@ shown in FIGURE 3.

A plurality of support flanges 22 are formed in the outer wall of the cylindrical portion 20a at the respective sides and top of the cover 20 at approximately 90 degree spacings to permit the cover 20 to be supported, at least in part, directly by the support frame 12. As best seen in FIGURE 5, each of the support flanges 22 include a mounting plate 23 secured to the respective sides thereof by a pair of bolts 24 and associated mating nuts (not shown). A portion of the mounting plates 23 extend outboard of the associated support flange 22 to permit :51 rotatably adjustable turn-buckle 25 to be secured between such outboard portion of the mounting plates 23 and a pipe clamp 26 securely fastened to the support member 12a by bolts 27 in the manner shown.

The cover 20 is also supported on the reflector dish 11 and rigidly held in place thereon by a plurality of mounting clamps 30 intermittently spaced around the periphery of the dish 11. As best seen in FIGURE 4, each of the mounting clamps 30 includes a bottom U-shaped member 31 underlying the dish lip portion 11a and a top L-shaped member 32 overlying the top of the cover flange portion 200 and extending downward beyond the depending rim 29:1 to abut against the bottom member 31. A bolt 33 passes through suitable clearance holes provided in the members 31 and 32 to mate with an associated nut 34, which when drawn up tightly, securely fastens the flange portion 200 of the radome cover 20 to the lip portion 11a of the reflector dish 11.

Thus it is seen that the radome cover 20 provides a weather-tight enclosure for the front of the reflector dish 11 and the energizing waveguide section 15 to protect the same from severe environmental conditions such as hi h winds, rain, sleet, snow and ice which might otherwise etfect undesired variations in the energizing of the antenna and thereby seriously impair the performance characteristics thereof. The cover 20 presents a light weight, self-supporting and mechanically rigid structure which requires little, if any, additional superstructure or bracing on the antenna support frame to adequately support the weight of the cover. Such characteristics stem not only from the epoxy resin construction with re-inforced fiberglass base, but also from the physical conformation of the cover 20 itself. As seen in FIGURE 7, the force exerted on the forward face of the cover 20 from wind loading is represented by the plurality of solid arrows. Due to the outward conical conformation of this face, such force is vectored diagonally, as represented by the arrows shown in dotted lines, toward the rim or top peripheral edge of the cylindrical portion 20a, indicated generally by the symbol A. Thus, such rim portion A is effectively placed in hoop expansion, and the entire structure is seen to possess a high degree of mechanical rigidity superior to that provided if the face of the cover 20 was merely of a flat configuration. In the latter case, it will be seen that the forces acting on the peripheral edge would tend to collapse such edge or rim inwardly.

While the cover 20 thus provides protection from the deteriorating effects of adverse weather conditions, it cannot, without more, effect any improvement in the radiation performance characteristics inherent in the antenna 10. Due to practical considerations, there are always a certain amount of variations in the energizing of the reflector dish 11 from other than the precise focal point as well as some imperfections which will occur in the reflector dish 11 itself. For illustrative purposes, typical side and back radiational patterns due to such imperfections and feed variations are depicted in FIGURE 6a.

To improve the radiation directional pattern of the antenna 10, a conductive facing is provided for the entire interior surface of the cylindrical portion 200 to act as a reflecting shroud. It is understood that such conductive facing may be provided in a number of ways, such as using a metalized paint to coat the interior surface or by employing a tape having an adherent on one side and a metallic coating on the other. The preferred embodiment, however, and as shown in FIGURE 3, cmploys aluminum sheeting of relatively thin-gauge, viz. on the order of .016", for the shroud 40 so as to insure an optimum reflecting surface for the desired degree of efliciency and yet be relatively light in weight. The shroud 40 is preferably secured to the interior surface of the cylindrical portion 20a by riveting the same at intermediate spacings along the respective edges. The shroud 40 is operative to reduce side and back radiations by refleeting any electromagnetic energy incident on its surface.

Notwithstanding the use of such reflecting shroud 40, it has been found that radiation leakage will occur at any point where there is a gap in direct physical contact between the dish 11 and the shroud 40. In most instances, such leakage radiation is substantial and suflicient to effectively nullify any improvements in the side radiational pattern otherwise gained by the use of a reflecting shroud 40. To insure that no such disruptive leakage radiation occurs between the dish 11 and the shroud 40', a multilayer conductive mesh 45 is provided on the upperside of the flange portion 200. Preferably, such conductive mesh includes at least four layers. An underlay of rubber stripping 46 is included to provide a resilient support for the conductive mesh 45 whereby positive and continuous electrical continuity is established at all points around the periphery of the dish 11 despite any dimensional variations or the like which might be encountered in the various component parts. The mesh 45 is secured to the shroud 40 by inserting a portion thereof between the wall of the cylindrical portion 202: and a top portion of the shroud 40 before riveting a strap 47 on the upper edge in the manner shown in FIGURE 3. The mesh 45 is held in place on the surface of the flange portion 200 by an additional strap riveted along the inner surface of the rim 20d.

The interior surface of the housing extension 20c is also lined with a like conductive mesh 49 which is suitably secured to the shroud by overlying corner brackets 50 suitably riveted to the cover 20 and shroud 40. The conductive mesh 45 and 49 is preferably formed from aluminum screening which, being the same material as the dish 11 and the shroud 40, prevents any galvanic currents, and the attendant corrosion, which would otherwise occur if dissimilar metals were to be used.

The resultant establishment of electrical continuity between the shroud 40 and the dish 11 at all points around the periphery thereof insures that no leakage radiation will occur from therebetween and the reflecting shroud 40 reflects back all electromagnetic energy incident on its surface to further suppress radiation to the side and rear. The resultant improvement in side and back directional radiation pattern over that without the shroud 40 is shown in FIGURE 6b.

As mentioned above, the cover means 20 may be of two-part construction so that it can be knocked down for shipment. It is assembled in unitary form, however, before use and acts as a unitary structure in the product as used. The term unitary is used in the appended claims to designate the structure whether in one piece or two, so long as it is assembled in one unit and so acts in the completed structure.

It will be understood that, while a specific antenna construction embodying the present invention is shown and described herein, various modifications therefrom may be made without departing from the true scope of the invention.

What is claimed is:

1. A high frequency antenna of paraboloid configuration, comprising; a parabolic dish reflector having a concave reflecting surface and a marginal flange, energizing means to radiate electromagnetic energy onto said surface from a point forwardly thereof for reflection as a sharply defined beam, unitary cover means constructed of low loss, light weight, non-metallic material having a marginal conformation to seat on said dish flange, said cover means having a cylindrical portion extending from the periphery of said dish reflector to a point beyond the confines of said energizing means, said cover means further having an imperforate web portion integral with the cylindrical portion spanning the forward end thereof to define a weather-tight enclosure for the reflector surface, said web portion protruding outwardly towards the center to present a generally conical conformation so as to substantially reduce wind loading and form a mechani cally rigid structure, and a conducting facing on the interior surface of said cylindrical portion operative to function as a reflecting shroud and improve the radiation directional pattern of said antenna.

2. A high frequency antenna of paraboloid configuration, com-prising; a circular dish reflector having a concave reflecting surface with an outturned lip portion around the periphery thereof, energizing means to radiate electromagnetic energy onto said surface from a point forwardly thereof for reflection as a sharply defined beam, unitary cover means constructed of a light weight, low loss non-metallic material for enclosing the face of said dish reflector and having a marginal flange extending radially therefrom for seating on said dish lip portion, said cover means having a cylindrical portion extending outwardly to a distance beyond the confines of said energizing means, said cover means further having an imperforate web portion integral with said cylindrical portion spanning the forward end thereof to define a weather tight enclosure, said web portion having a generally convex outwardly, conical conformation to reduce wind loading, a conducting facing on the interior surface of said cylindrical portion formed of relatively thin-gauge aluminum sheeting supported by said cylindrical portion for acting as a reflecting shroud to improve radiation directional pattern of said antenna, and a resilient annulus sandwiched between said marginal cover flange and said outturned lip, and at least one layer of conductive mesh having opposing longitudinal edges affixed to said cover flange outboard said outturned lip and to said conducting facing, respectively, and interposed between the outturned lip and said resilient annulus to prevent leakage radiation.

3. A high frequency antenna of paraboloid configuration, comprising; a circular dish reflector having a concave reflecting surface and an outboard marginal dish flange, energizing means to radiate electromagnetic energy onto said surface from a point forwardly thereof for reflection as a sharply defined beam, a weather tight cover of unitary construction for enclosing the face of said reflector dish, said cover being formed of a low loss, light weight, non-metallic material, said cover including a cylindrical portion having a marginal flange extending radially from the base thereof to seat on said dish flange, said marginal cover flange having a cylindrical upstanding outer lip, said cylindrical portion extending in the axial direction from the periphery of said dish reflector to a point beyond the confines of said energizing means, said cylindrical portion having an imperforate web spanning the forward end thereof to define said weather tight cover, a conductive facing on the interior surface of said cylindrical portion operative to reflect radiant energy and improve the radiation directional pattern of the antenna, a resilient annulus sandwiched between said marginal dish flange and said marginal cover flange, and at least four layers of conductive mesh having respective opposing sides aflixed to the interior of the cylindrical portion adjacent the marginal cover flange and to the upstanding outer lip and extending across the resilient annulus between the same and the outturned marginal dish flange.

4. A weather tight, low loss radome cover of unitary construction for enclosing the face of a parabolic antenna dish reflector having an outturned lip portion around the periphery thereof, including in combination; a cylindrical portion having a flange extending radially from the base and having a cylindrical upstanding outer lip, said cylindrical portion extending in the axial direction from the periphery of said dish reflector to a point beyond the focal point of said dish reflector, said cylindrical portion having an imperforate web spanning the forward end to define a weather tight enclosure, a conductive facing on the interior surface of said cylindrical portion operative as a reflecting shroud to reflect radiant energy incident thereon and improve the radiation directional pattern, and a resilient annulus sandwiched between said outturned lip of said dish and said cover flange, and at least one layer of conductive mesh having opposing longitudinal edges affixed to said outer lip of said cover flange and to said conductive facing respectively, and interposed between said outturned lip of said dish and said resilient annulus, said cover flange seating on said outturned lip of said dish with said resiliently supported conductive mesh insuring positive and continuous electrical continuity between said conductive facing and all points around the periphery of said reflector dish, thereby preventing leakage radiation from occurring therebetween.

5. A high frequency antenna of paraboloid configuration, comprising; a circular dish reflector having a concave reflecting surface with an outturned lip portion around the periphery thereof, energizing waveguide means to radiate electromagnetic energy onto said surface from a point forwardly thereof for reflection as a sharply defined beam, unitary cover means constructed of a plastic material with a reinforced fiberglass base for light weight, low loss and a high degree of mechanical rigidity for enclosing the face of said dish reflector and waveguide means, said cover means including a cylindrical portion having a marginal flange extending radially from one end with a cylindrical upstanding outer lip, said cylindrical portion extending in the axial direction to at least the focal point of said dish reflector, said cylindrical portion having an imperforate web portion spanning the forward end and integral therewith to form a weather tight enclosure, said web portion having a general convex outwardly, conical conformation to reduce Wind loading, a feed clearance chute depending mm the base of said cover means having an opening therein for receiving said energizing waveguide means therethrough, means for securing said cover flange to said outturned lip of said dish, including a plurality of peripherally spaced mounting clamps, a conductive facing formed of relatively thin gauge aluminum sheeting supported by said cylindrical portion on the interior surface thereof and effective as a reflecting shroud to improve the radiation directional pattern of said antenna, and shielding means for preventing leakage radiation to the side and back, said shielding means including at least four layers of aluminum screening with an underlay of resilient, rubberlike material, said screening having opposing longitudinal edges aflixed to said outer lip of said cover flange and to said conductive facing, respectively, said shielding means further including additional aluminum screening lining the interior surface of said feed clearance chute.

References Cited FOREIGN PATENTS 6/1957 Germany.

OTHER REFERENCES ELI LIEBERMAN, Primary Examiner. 

1. A HIGH FREQUENCY ANTENNA OF PARABOLOID CONFIRGUATION, COMPRISING; A PARABOLIC DISH REFLECTOR HAVING A CONCAVE REFLECTING SURFACE AND A MRAGINAL FLANGE, ENERGIZING MEANS TO RADIATE ELECTROMAGNETIC ENERGY ONTO SAID SURFACE FROM A POINT FORWARDLY THEREOF FOR REFLECTION AS A SHARPLY DEFINED BEAM, UNITARY COVER MEANS CONSTRUCTED OF LOW LOSS, LIGHT WEIGHT, NON-METALLIC MATERIAL HAVING A MARGINAL CONFORMATION TO SEAT ON SAID DISH FLANGE, SAID COVER MEANS HAVING A CLYINDRICAL PORTION EXTENDING FROM THE PERIPHERY OF SAID DISH REFLECTOR TO A POINT BEYOND THE CONFINES OF SAID ENERGIZING MEANS, SAID COVER MEANS FURTHER HAVING AN IMPERFORATE WEB PORTION INTEGRAL WITH THE CLYINDRICAL PORTION SPANNING THE FORWARD END THEREOF TO DEFINE A WEATHER-TIGHT ENCLOSURE FOR THE REFLECTOR SURFACE, SAID WEB PORTION PROTRUDING OUTWARDLY TOWARDS THE CENTER TO PRESENT A GENERALLY CONICAL CONFORMATION SO AS TO SUBSTANTIALLY REDUCE WIND LOADING AND FORM A MECHANICALLY RIGID STRUCTURE, AND CONDUCTING FACING ON THE INTERIOR SURFACE OF SAID CYLINDRICAL PORTION OPERATIVE TO FUNCTION AS A FEFLECTING SHROUD AND IMPROVE THE RADIATION DIRECTIONAL PATTERN OF SAID ANTENNA. 